JP5350328B2 - Distance sensor and control method - Google Patents

Description

  The present invention relates to a distance sensor that calculates a measurement distance to a measurement object based on a phase difference between a transmitted wave and a reflected wave.

  In the phase-type distance sensor, the distance to the measurement object is calculated from the phase difference between the transmission wave and the reflected wave reflected by the measurement object (see, for example, Patent Document 1).

JP-A-8-88672

  In a phase-type distance sensor, the maximum distance (so-called “distance range”) that can be measured is determined by the frequency of the transmission wave. Specifically, the lower the frequency, the longer the wavelength, and the greater the distance range. On the other hand, in order to measure the distance with high accuracy, it is necessary to set the frequency of the transmission wave to a high frequency. That is, depending on the actual distance to the object to be measured, the distance can be measured, and the distance range considered to have the best measurement accuracy differs. Therefore, how to switch the distance range and how to detect an appropriate distance range are problems.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to realize switching of a new distance range in a phase-type distance sensor. The second purpose is to enable detection of an appropriate distance range.

The first form for solving the above problem is
A frequency divider (for example, frequency divider 4 in FIG. 3) capable of changing a frequency dividing ratio for dividing a clock signal having a predetermined reference frequency (for example, clock signal F1 in FIG. 3); A transmission unit (for example, the light emitting unit 6 in FIG. 3) that generates and transmits a transmission wave from the frequency-divided signal divided by
A receiving unit (for example, the light receiving unit 16 in FIG. 3) that receives a reflected wave of the transmission wave;
A control unit that changes the wavelength division ratio of the frequency divider to change the wavelength of the transmission wave, and calculates a measurement distance to the measurement object based on a phase difference between the transmission wave and the reflected wave ( For example, the control unit 30) of FIG.
Is a distance sensor (for example, the distance sensor 100 of FIG. 3).

  According to the first aspect, in the distance sensor that calculates the measurement distance to the measurement object based on the phase difference between the transmitted wave and the reflected wave, the frequency signal is obtained by dividing the clock signal having a predetermined reference frequency. Although a transmission wave is generated, the frequency division ratio of the frequency divider that divides the clock signal is changed and controlled. As described above, the frequency of the transmission wave, that is, the distance range can be easily changed only by changing and controlling the frequency dividing ratio of the frequency divider. Further, since it is only necessary to change and control the frequency division ratio of the frequency divider, only one oscillator having a fixed oscillation frequency is required as the transmission wave oscillator.

As a second form, the distance sensor of the first form,
A suitable distance range suitable for measurement when the division ratio is used for each division ratio is determined in advance (for example, the division ratio switching table 32 in FIG. 5).
The control unit repeatedly performs the change control of the division ratio and the calculation of the distance so that the division ratio becomes a division ratio corresponding to the suitable distance range including the measurement distance.
A distance sensor may be configured.

  According to the second embodiment, a suitable distance range suitable for measurement when the frequency division ratio is set is determined in advance for each frequency division ratio of the frequency divider, and the frequency division ratio preferably includes the measurement distance. The division ratio change control and the distance calculation are repeatedly performed so that the division ratio corresponds to the distance range. That is, the distance range is changed to a suitable distance range according to the calculated measurement distance.

Specifically, as a third form,
The control unit temporarily calculates the measurement distance by changing the division ratio to a changeable maximum value, and changes the division ratio to a suitable division range including the provisionally calculated measurement distance. Calculate the measurement distance,
A distance sensor may be configured.

As another form,
A transmitter having a frequency divider capable of changing a frequency dividing ratio for dividing a clock signal having a predetermined reference frequency, and a transmitter that generates and transmits a transmission wave from the frequency-divided signal divided by the frequency divider; A distance meter control method comprising a receiving unit that receives a reflected wave of the transmission wave,
A provisional measurement step of provisionally measuring the measurement distance by changing the division ratio to a maximum changeable value;
A main measurement step of performing main measurement by changing the division ratio based on the measurement distance temporarily measured in the temporary measurement step;
A distance meter control method including the above may be configured.

  According to the third aspect and the like, the measurement distance is provisionally calculated by changing the division ratio of the frequency divider to the maximum value that can be changed, and the frequency division corresponding to the preferred distance range including the provisionally calculated measurement distance Change to the ratio and calculate the measurement distance again. In other words, first, provisional measurement is performed in the maximum distance range, and then the measurement distance in the provisional measurement is changed to the optimum distance range to perform the main measurement. Thereby, an appropriate distance range can be detected efficiently and can be measured.

As a fourth form, the distance sensor of any one of the first to third forms,
The receiver is
A reference signal frequency divider (for example, the frequency divider 10 in FIG. 3) that divides a reference clock signal (for example, the reference clock signal F2 in FIG. 3) having a predetermined reference frequency;
A first frequency converter (for example, the mixer of FIG. 3) that down-converts the frequency of the frequency-divided signal divided by the frequency divider using the reference frequency-divided signal frequency-divided by the reference signal frequency divider. 12)
A first filter unit (e.g., LPF 14 in FIG. 3) that extracts a down-converted frequency band signal from the signal converted by the first frequency conversion unit;
A second frequency converter (for example, the mixer 18 in FIG. 3) that down-converts the frequency of the received reflected wave using the reference divided signal;
A second filter unit (e.g., LPF 20 in FIG. 3) that extracts a down-converted frequency band signal from the signal converted by the second frequency conversion unit;
Have
The control unit uses the signal extracted by the first filter unit as the transmission wave and the signal extracted by the second filter unit as the reflected wave, and determines the measurement distance based on the phase difference between the two waves. calculate,
A distance sensor may be configured.

  According to the fourth embodiment, a signal obtained by down-converting the frequency-divided signal divided by the frequency divider using the reference frequency-divided signal obtained by frequency-dividing the reference clock signal having a predetermined reference frequency is used as the transmission wave. At the same time, using this reference frequency-divided signal, a signal obtained by down-converting the frequency of the reflected wave is used as a reflected wave, and the measurement distance is calculated based on the phase difference between the transmitted wave and the reflected wave. That is, the measurement distance is calculated based on the phase difference of the signals obtained by down-converting the transmission wave and the reflected wave with the same reference frequency-divided signal. Thereby, the calculation accuracy of the measurement distance can be improved.

As a fifth form, the distance sensor of the fourth form,
The reference signal divider can change a division ratio;
The control unit is configured to change and control the frequency division ratio of the frequency divider and the frequency division ratio of the reference signal frequency divider,
A distance sensor may be configured.

Further, as a sixth form, the distance sensor of the fourth or fifth form,
The first and second filter units can change the frequency passband;
The control unit changes and controls the frequency dividing ratio of the frequency divider and the passbands of the first and second filter units;
A distance sensor may be configured.

The schematic diagram of a distance sensor. Explanatory drawing of the difference in the measurement precision by a transmission frequency. The block diagram of a distance sensor. Explanatory drawing of the improvement of the measurement precision by down-conversion of a transmission signal and a received signal. The data structural example of a division ratio switching table. An example of the correspondence of a frequency division ratio and a suitable distance range. The flowchart of a distance measurement process. The flowchart of another distance measurement process. Explanatory drawing of the measurement of the distance which exceeds the half wavelength of a transmission frequency. An example of variable frequency division ratio.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, a lightwave distance sensor to which the present invention is applied will be described, but embodiments to which the present invention can be applied are not limited thereto.

[Overview]
FIG. 1 is a schematic diagram of distance measurement by the distance sensor 100 in the present embodiment. This distance sensor 100 is a light wave distance sensor using light waves such as infrared rays and laser light, and measures the distance L to the measuring object 200 by a phase method.

That is, as shown in FIG. 1A, a transmission wave that is a light wave is emitted toward the measurement object 200, and the reflected wave reflected by the measurement object 200 is received. Then, as shown in FIG. 1B, the distance L to the measuring object 200 is calculated from the delay time tx (phase difference) between the transmitted wave and the received reflected wave. The distance L to the measurement object 200 is calculated as L = (C · tx) / 2. Here, “C” is the speed of light, and C≈3 × 10 ⁸ m / s.

  Further, in order to calculate the distance L from the delay time tx between the transmission wave and the reflected wave, when calculating the distance L with only one transmission frequency, the delay time tx needs to be within one cycle of the transmission frequency. is there. For this reason, the maximum measurable distance Lm (so-called “distance range”) is theoretically determined by the frequency f of the transmission wave and is Lm = λ / 2 = C / (2 · f). For example, when the frequency of the transmission wave is “50 MHz”, the wavelength λ is “6 m” and the maximum measurable distance Lm is “3 m”.

  The calculation accuracy of the measurement distance L by the phase-type distance sensor differs depending on the frequency of the transmission wave. Specifically, the calculation accuracy is better as the frequency of the transmission wave is higher.

  FIG. 2 is a diagram for explaining the difference in calculation accuracy of the measurement distance L due to the difference in the frequency of the transmission wave. In the drawing, the upper side shows a transmission wave and a reception wave having a frequency fa, and the lower side shows a transmission wave and a reception wave having a frequency fb (= 3 · fa) higher than the frequency fa.

  When measuring the same distance L, the delay time tx between the transmission wave and the reflected wave is the same regardless of the frequency f of the transmission wave, but the wavelength λ differs depending on the frequency f. The phase difference φ is different. Specifically, the higher the frequency, the larger the phase difference φ corresponding to the same delay time tx. In FIG. 2, the phase difference φb at the frequency fb is larger than the phase difference φa at the frequency fa, and φb = 3 · φa.

  When detecting the phase difference φ between two signals, the smaller the phase difference φ, the easier the detection error. That is, as the frequency f of the transmission wave is lower, a detection error of the phase difference φ is more likely to occur, and the calculation accuracy of the measurement distance L is reduced. In other words, as the frequency f of the transmission wave is higher, the detection error of the phase difference φ is less likely to occur and the calculation accuracy of the measurement distance L is improved.

[Constitution]
FIG. 3 is a configuration diagram of the distance sensor 100 of the present embodiment. As shown in FIG. 3, the distance sensor 100 includes an oscillator 2, frequency dividers 4 and 10, a light emitting unit 6, a PLL 8, mixers 12 and 18, LPFs 14 and 20, a light receiving unit 16, and a control unit. 30.

  For example, the oscillator 2 includes a crystal resonator and generates a clock signal F1 having a reference frequency f1. The reference frequency f1 is, for example, “50 MHz”.

The frequency divider 4 divides the frequency f1 of the clock signal F1 output from the oscillator 2 by 1 / N and outputs it as a transmission signal V _T. The frequency division ratio N of the frequency divider 4 is “N = 2 ⁿ (n is a positive number)”, and is changed and controlled by the control unit 30.

Emitting unit 6 is composed of, for example, a light-emitting element such as a laser diode, an optical signal whose intensity is modulated at a frequency of the transmitted signal V _T output from the frequency divider 4, and emits a transmission wave.

  The PLL 8 generates a reference clock signal F2 having a reference frequency f2 lower than the reference frequency f1. This reference frequency f2 is, for example, “49.9 MHz” when the reference frequency f1 is “50 MHz”.

  The frequency divider 10 divides the frequency f2 of the reference clock signal F2 generated by the PLL 8 by 1 / N and outputs it as a reference frequency division signal. The frequency division ratio N of the frequency divider 10 is the same as the frequency division ratio N of the frequency divider 4 and is varied by the control unit 30.

The mixer 12 includes a transmission signal V _T output from the frequency divider 4, a reference frequency-divided signal output from the frequency divider 10 Synthesis (mixing) and outputs. The output signal of the mixer 12 includes a signal having a difference frequency and a sum frequency “(f1 ± f2) / N” between the transmission signal _VT and the reference divided signal.

The LPF 14 passes a predetermined low-band signal with respect to the output signal of the mixer 12, cuts off a frequency component outside the band, and outputs the signal as a transmission modulation signal Vs. The cut-off frequency fc of the LPF 14 is passed through the signal component of the difference frequency “(f1−f2) / N” between the transmission signal _VT and the reference frequency-divided signal by the control unit 30, and the sum frequency “(f1 + f2) / N ”is set to fc = 2 (f1−f2) / N so as to cut off the signal component. That is, the transmission modulation signal Vs output from the LPF 14 is a signal obtained by down-converting the transmission signal _VT with the reference frequency-divided signal.

Light receiving unit 16 is configured, for example, a light receiving element such as a photodiode, and converts the received optical signal into an electric signal, and outputs as a reception signal V _R.

The mixer 18 synthesizes the received signal V _R output from the light receiving unit 16, and a reference frequency-divided signal output from the divider 10 (multiplication). This output signal of the mixer 18 includes signals of the sum and difference frequencies between the reference frequency-divided signal and the received signal V _R '(f1 ± f2) / N "is.

The LPF 20 passes a predetermined low-band frequency with respect to the output signal of the mixer 18, cuts off a frequency component outside the band, and outputs it as a reception modulation signal Vx. Cut-off frequency fc of the LPF20 is, the control unit 30, the signal component of the difference frequency between the reference frequency-divided signal and the received signal _{V R} '(f1-f2) / N "is passed, the sum frequency" (f1 + f2) / N ”is set to fc = 2 (f1−f2) / N so as to cut off the signal component. That is, the received modulated signal Vx output from the LPF20 the received signal V _R is a received wave, a signal obtained by down-converting the reference frequency-divided signal.

  The control unit 30 includes an arithmetic device such as a CPU, and executes a distance measurement process for measuring the distance L to the measurement object. In this distance measurement process, first, the frequency division ratio N of the frequency dividers 4 and 10 is set to the maximum value Nmax. Further, the cut-off frequency fc of the LPFs 14 and 20 is set in accordance with the set frequency division ratio N. The cut-off frequency fc is given by fc = 2 (f1−f2) / N.

  Next, the distance L to the measurement object is measured. That is, the delay time tx between the transmission modulation signal Vs and the reception modulation signal Vx is measured, the distance L is calculated from this time difference tx, and is set as the initial measurement distance Lx. The measurement distance L is calculated by L = (C / m) · tx) / 2. Here, “m” is given by m = f1 / (f1−f2).

Here, instead of the transmission signal V _T and the received signal V _R, the delay time tx between the received modulated signal Vx and the transmission modulation signal Vs is measured, by calculating the measured distance L, the measurement accuracy (calculation of the measurement distance L Accuracy) can be improved.

Figure 4 is a diagram for explaining the improvement in measurement accuracy of the measurement distance L by the down-conversion of the transmission signal V _T and the received signal V _R. In the figure, the upper shows the signal waveform of the transmission signal V _T and the received signal V _R, the lower side shows the signal waveform of the modulated transmission signal Vs and the received modulation signal Vx.

As shown in FIG. 4, the frequency of the transmitted signal _{V T} and the received signal _{V R} is "f1 / N", the frequency of the modulated transmission signal Vs and the received modulation signal Vx is the "(f1-f2) / N" . In other words, the modulated transmission signal Vs and the received modulation signal Vx, respectively, equivalent to the transmission signal V _T and the received signal V _R and 1 / m divider. However, m = f1 / (f1-f2). In other words, the modulated transmission signal Vs and the received modulation signal Vx, respectively, "expansion" signal of the transmission signal V _T and the received signal V _R in the time axis direction, i.e., corresponds to a signal with a reduced speed of light c. Accordingly, time delay tx of the transmit signal V _T and the received signal V _R has also been "expanded".

Thus, it is sufficient to detect the time delay tx of the transmit modulation signal Vs corresponding to the time lag tx0 the transmitting signal V _T and the received signal V _R and the received modulation signal Vx, it improves the detection accuracy of the delay time tx As a result, the calculation accuracy of the measurement distance L is improved. In particular, as the delay time tx is smaller, the detection accuracy is significantly improved.

  Subsequently, the optimum frequency division ratio N corresponding to the initial measurement distance Lx is determined according to the frequency division ratio switching table 32 stored in the control unit 30.

  FIG. 5 is a diagram illustrating an example of a data configuration of the frequency division ratio switching table 32. As shown in FIG. 5, the frequency division ratio switching table 32 stores a frequency division ratio 32 a that can be set in the distance sensor 100 and a suitable distance range 32 b in association with each other. “E” that defines the preferred distance range 32b is an error margin that represents an error to be estimated with respect to the measurement distance L, and is a value of “0.0 <e ≦ 1.0”. Given to. For example, the error margin e = 0.9 represents that an error of “10% (= 0.1 = 1.0−0.9)” with respect to the measurement distance L is included.

  The control unit 30 determines that the frequency division ratio N corresponding to the preferred distance range including the initial measurement distance Lx is the optimum frequency division ratio N. Then, the frequency division ratio N of the frequency dividers 4 and 10 is changed to the frequency division ratio N determined to be optimal, and the cutoff frequency fc of the LPFs 14 and 20 is changed in accordance with the frequency division ratio N after the change. . Thereafter, the time difference Tx between the transmission modulation signal Vs and the reception modulation signal Vx is remeasured, the distance L to the measurement object is recalculated, and the measurement result is output.

  The correspondence relationship between the “frequency division ratio N” and the “preferred distance range” determined in the frequency division ratio switching table 32 is determined as follows.

  FIG. 6 is a diagram illustrating an example of a correspondence relationship between the frequency division ratio N and the preferred distance range. FIG. 6 shows, in order from the top, cases of error margin e = 1.0, error margin e = 0.9, and error margin e = 0.5. However, the settable division ratio N is “N = 1, 2, 4, 8, 16”, and the reference frequency f1 is “f1 = 50 MHz”.

  As shown in FIG. 6, a suitable distance range that does not overlap each other is associated with each settable division ratio N. This preferred distance range is determined according to the distance range of the frequency division ratio N and the error expected for the distance measured by the distance sensor 100.

  That is, when an error is not expected (error margin e = 1.0), the preferred distance range corresponding to a certain frequency division ratio N has a maximum distance range at the frequency division ratio N, and is one level lower than that. It is determined as a range in which the distance range at the circumferential ratio N (= N / 2) is the minimum value.

  For example, the distance range of the frequency division ratio N = 16 is “48 m”, and the distance range of the frequency division ratio N = 8 is “24 m”. Accordingly, “24 to 48 m” is associated with the frequency division ratio N = 16 as the preferred distance range.

  Similarly, “12 to 24 m” is associated with the frequency division ratio N = 8 as a suitable distance range, and “6 to 12 m” is associated with the frequency division ratio N = 4 as the suitable distance range. “3 to 6 m” is associated with the circumferential ratio N = 2 as a preferred distance range, and “0 to 3 m” is associated with the circumferential ratio N = 1 as the preferred distance range.

  When the error is expected, the error is changed to the expected value in the minimum value and the maximum value of the preferable distance range when the error is not expected (error margin e = 1.0).

  For example, when an error of “50%” is expected with respect to the measurement distance L (error margin e = 0.5), the frequency division ratio N = 16 (maximum value Nmax) is preferable when no error is expected. “12 m (= 24−24 × 0.5)” that allows for an error of “50%” with respect to “24 m” that is the minimum value of the distance range is set as the minimum value. That is, “12 to 48 m” is associated with the frequency division ratio N = 16 as a preferable distance range.

  For the next largest division ratio N = 8 (= 16/2), the maximum value of the preferred distance range is set to the division ratio N = 16 so as not to overlap with the preferred distance range of the division ratio N = 16. The minimum value is “12 m”, and the minimum value is “6 m (= 12−12 × 0.5)” with an error of “50%” compared to the minimum value “12 m” when no error is expected. To do. That is, “6 to 12 m” is associated with the frequency division ratio N = 8 as the preferred distance range.

  Similarly, the frequency division ratio N = 4 is associated with “3 to 6 m” as the preferred distance range, and the frequency division ratio N = 2 is associated with “1.5 to 3 m” as the suitable distance range. The frequency division ratio N = 1 is associated with “0 to 1.5 m” as a preferred distance range.

  Here, as a processing procedure in the present embodiment, the priority distance range of the maximum value Nmax of the frequency division ratio N is given priority over the correspondence between the frequency division ratio N and the suitable distance range in which an error is expected. This is because, after setting the frequency division ratio N of the frequency dividers 4 and 10 to the maximum value Nmax, the optimum frequency division ratio N is judged and changed.

[Process flow]
FIG. 7 is a flowchart for explaining the flow of the distance measurement process executed by the control unit 30. According to FIG. 7, the control unit 30 first sets the frequency division ratio N of each of the frequency dividers 4 and 10 to the maximum value Nmax (step A1). Further, the cutoff frequencies fc of the LPFs 14 and 20 are set in accordance with the set frequency dividing ratio N (step A3).

  Next, a delay time tx (phase difference) between the transmission modulation signal Vs and the reception modulation signal Vx is measured (step A5), and an initial measurement distance Lx is calculated based on the delay time tx (step A7). Subsequently, the optimum frequency division ratio N corresponding to the calculated initial measurement distance Lx is determined with reference to the frequency division ratio switching table 32 (step A9). Then, the frequency division ratio N of each of the frequency dividers 4 and 10 is updated to the frequency division ratio N determined to be optimal (step A11), and the LPFs 14 and 20 are cut in accordance with the frequency division ratio N after the update. The off frequency fc is updated (step A13).

  Thereafter, the delay time tx between the transmission modulation signal Vs and the reception modulation signal Vx is remeasured (step A15), and the measurement distance L is recalculated based on the delay time tx (step A17).

[Action / Effect]
As described above, the distance sensor 100 according to the present embodiment uses the frequency division ratio N of the frequency divider 4 that divides the reference clock signal F1 generated by the oscillator 2 by 1 / N and the reference clock signal F2 generated by the PLL 8 as 1. The frequency dividing ratio N of the frequency divider 10 that divides / N is variable. When performing distance measurement, first, the frequency division ratio N of each of the frequency dividers 4 and 10 is set to the maximum value Nmax, and each of the frequency dividers 4 and 10 is set according to the measurement distance Lx calculated at this time. After changing the frequency division ratio N to the optimum frequency division ratio N, the measurement distance is calculated again. Thereby, automatic switching of an appropriate distance range according to the actual distance to the measuring object 200 is realized.

[Modification]
It should be noted that embodiments to which the present invention can be applied are not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention.

(A) Switching of frequency dividing ratio For example, switching of the frequency dividing ratio N of each of the frequency dividers 4 and 10 in the distance sensor 100 may be changed so as to be decreased step by step.

  FIG. 8 is a flowchart of the distance measurement process when the frequency division ratio N is changed step by step. As shown in FIG. 8, first, the frequency division ratio N of each of the frequency dividers 4 and 10 is set to the maximum value Nmax (step B1), and the LPFs 14 and 20 are cut in accordance with this frequency division ratio N. The off frequency fc is set (step B3).

  Next, the delay time tx between the transmission modulation signal Vs and the reception modulation signal Vx at this time is detected (step B5), and the measurement distance Lx to the measurement object is calculated based on the detected delay time tx (step B5). B7). Then, the current frequency division ratio N is “2” or more (step B9: YES), and the calculated measurement distance Lx is the minimum value “(N / 2) · Lmin · e ”or less (step B11: YES), the frequency division ratio N is changed to be decreased by one step (step B13). Thereafter, the process returns to step B3, and similarly, the measurement distance to the measurement object is recalculated.

  On the other hand, when the current frequency division ratio N becomes “1” (step B9: NO), or the calculated measurement distance Lx is the minimum value “(N of the preferred distance range corresponding to the current frequency division ratio N” / 2) · Lmin · e ”(step B11: NO), it is determined that the current division ratio N is a suitable division ratio N (step B15), and the measurement distance Lx calculated at the end is determined. Is output as a measurement result.

For example, when measuring a short distance L, it is expected that the calculation error of the measurement distance L at the maximum frequency division ratio Nmax is large, and there is a possibility that the optimum frequency division ratio N is erroneously detected. Therefore, by changing the division ratio N so that the distance range is lowered step by step in this way, the optimum division ratio N can be detected more accurately and the calculation error of the measurement distance L can be reduced. .

Furthermore, in this case, the distance range by changing the frequency division ratio N to decrease by one step, can also be measured for the distance L exceeding the half-wavelength lambda / 2 of the transmission signal V _T, more accurate Distance measurement is realized.

Figure 9 is a diagram for explaining the measurement of the distance L exceeding the half-wavelength lambda / 2 of the transmission signal V _T. In the figure, upper, a frequency f1 / N of the transmission signal _{V T} shows the case of the "frequency fa (wavelength [lambda] a)", the lower side, the frequency f1 / N of the transmission signal _{V T,} higher than the frequency fa " The frequency fb (wavelength λb) ”is shown.

  As described above, since the distance L to the measurement object is measured from the delay time tx (phase difference) between the transmission signal and the reception signal, the calculated distance L is L <λ / 2. That is, when the actual distance Ls is measured, as shown in the upper side, when Ls <(λa / 2), the calculated distance L is “Ls”, but as shown in the lower side, Ls> The distance L calculated at (λb / 2) is “Ls−λb / 2”.

However, in the process of changing the frequency division ratio N so as to lower the distance range step by step, it is determined whether or not the calculated measurement distance Lx is within the preferred distance range corresponding to the current frequency division ratio N. to be in (step B11 in FIG. 8), the actual distance Ls is, it is possible to determine whether more than half wavelength lambda / 2 of the transmission signal V _T. That is, it is the actual distance Ls to determine the lower limit of the frequency division ratio N does not exceed the half-wavelength lambda / 2 of the transmission signal V _T. Then, the measurement distance L in the frequency division ratio N below this lower limit, it is corrected by adding the wavelength lambda / 2 minutes distance of the transmitted signal V _T at that time, calculating a more accurate measurement distance L It becomes possible to do.

(B) Dividing ratio N
Further, the frequency division ratio N of the frequency dividers 4 and 10 may not be the same. In this case, since it is the frequency division ratio N1 of the frequency divider 4 that determines the frequency of the transmission wave, at least the frequency division ratio N1 of the frequency divider 4 is changed according to the measurement distance Lx, so that the optimum distance is obtained. Can be changed to range. On the other hand, the division ratio N2 of the frequency divider 10, since the transmission signal V _T and the delay time between the received signal V _R is to improve the detection accuracy of tx, it may be fixed or may be variable.

Min when the frequency dividing ratio N2 and fixed the frequency divider 10, a frequency divider 10 for down-converting the received signal V _R by the reference divider signal outputted from the frequency divider 4 dividing ratio N1 When the maximum value is “N1max”, the frequency division ratio N2 of the frequency divider 10 is determined so as to satisfy (f1 / N1max)> (f2 / N2).

  Similarly, when the frequency division ratio N2 of the frequency divider 10 is made variable, it is similarly changed so as to satisfy (f1 / N1)> (f2 / N2). In this case, for example, as shown in FIG. 10, the frequency division ratio N2 of the frequency divider 10 may be varied so that the frequencies of the transmission modulation signal Vs and the reception modulation signal Vx are always constant. By making the frequency of the transmission modulation signal Vs and the reception modulation signal Vx constant at all times, the control unit 30 can detect the phase difference (delay time tx) and process the calculation of the measurement distance L. And processing operations can be simplified.

(C) Distance sensor In the above-described embodiment, the distance sensor 100 is a light wave distance sensor. However, if the distance sensor is a phase type distance sensor such as a distance sensor using electromagnetic waves or ultrasonic waves, the present invention is similarly applied. Is applicable.

100 Distance Sensor 2 Oscillator, 4,10 Frequency Divider, 6 Light Emitting Unit, 8 PLL
12, 18 Mixer, 14, 20 LPF, 16 Light receiver 200 Measurement object

Claims (3)

A transmitter having a frequency divider capable of changing a frequency dividing ratio for dividing a clock signal having a predetermined reference frequency, and a transmitter that generates and transmits a transmission wave from the frequency-divided signal divided by the frequency divider;
A receiver for receiving a reflected wave of the transmission wave;
A control unit that changes a wavelength of the transmission wave by changing and controlling a frequency division ratio of the frequency divider, and calculates a measurement distance to a measurement object based on a phase difference between the transmission wave and the reflected wave; ,
Equipped with a,
The control unit determines whether or not a distance based on a phase difference between the transmission wave and the reflected wave exceeds a half wavelength of the transmission wave while performing control to gradually reduce the frequency division ratio. When it is determined that the wavelength has been exceeded, the distance based on the phase difference between the transmitted wave and the reflected wave at that time is added to the distance of the half wavelength to calculate the measurement distance,
Distance sensor. Every predetermined dividing ratio, a suitable suitable distance range for measurement in the case where with the division ratio is predetermined,
The control unit performs control to lower the division ratio step by step according to the predetermined division ratio, and the distance based on the phase difference between the transmission wave and the reflected wave corresponds to the current division ratio The lower limit of the division ratio is determined so that the distance does not exceed the half wavelength of the transmission wave by determining whether or not the preferred distance is within the range, and when the division ratio falls below the lower limit, The distance sensor according to claim 1, wherein the distance is determined to have exceeded a half wavelength of the transmission wave . A transmitter having a frequency divider capable of changing a frequency dividing ratio for dividing a clock signal having a predetermined reference frequency, and a transmitter that generates and transmits a transmission wave from the frequency-divided signal divided by the frequency divider; A distance meter control method comprising a receiving unit that receives a reflected wave of the transmission wave,
While controlling to gradually reduce the frequency division ratio, it is determined whether the distance based on the phase difference between the transmitted wave and the reflected wave exceeds the half wavelength of the transmitted wave, and determined that the half wavelength has been exceeded. A control method for controlling the distance meter to calculate the measurement distance by adding the half-wave distance to the distance based on the phase difference between the transmitted wave and the reflected wave at that time .

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